Arsenal edged an extra point clear at the top of the Premier League at the cost of a second-half sending-off for Mathieu Flamini in a topsy-turvy match that greatly undermined any confidence in the leaders maintaining that position for much longer. Having fallen behind, Arsenal rapped back to take the lead but never looked like fully subduing a buoyant Southampton.

Jose Fonte’s goal was a fitting culmination to an opening 20 minutes of almost complete Saints domination, for which the minor delay to Arsenal’s team bus as they travelled down the M3 could not even be partial mitigation. The Portuguese star scored his second goal of the season with a powerful header – aided perhaps by a clever nudge in the back of his marker Nacho Monreal – that the Gunners’ goalkeeper Wojciech Szczesny could only parry over his own goal-line.

It came from a foul by Per Mertesacker on Adam Lallana and a long, looped cross from the left by Luke Shaw from the subsequent free-kick.

There had been enough alarm bells ringing already to worry Arsenal, chief among them Lallana being allowed a free header from a corner that was fortuitously cleared by Oliver Giroud and a couple of slack dispossessions in midfield suffered by Monreal and Santi Cazorla.

There was also a snapshot by Sam Gallagher that Szczesny needed to beat out – but it could have been far worse for Arsenal on 35 minutes when the 18-year-old Gallagher, who scored on his first Saints start against Yeovil in the FA Cup last weekend, missed a sitter in the sheeting rain. The panicky Monreal had a clearance rebound off Steven Davis straight to the youngster on the edge of the six-yard box, but he side-footed wide.

Jose Fonte of Southampton turns to celebrate scoring the opening goal

Four minutes before half-time it needed a magnificent sliding block by Laurent Koscielny to deny a goal-bound shot by Gallagher. When Arsène Wenger praised the Southampton production line of young players pre-match, he may have tempted too much fate.

In transfer window week, Southampton – whose relatively poor league run of late could be traced back to losing the reverse fixture at Arsenal in November – have been more concerned with outs than ins. There are those who hope the seemingly inevitable departure of Shaw will be delayed until the summer as an act of appeasement by owner Katharina Liebherr towards the Saints’ manager , Mauricio Pochettino, after the recent departure of chairman Nicola Cortese. Record signing Dani Osvaldo, however, looks set to leave sooner rather than later after an unsavoury incident with Fonte in training last week.

Arsenal's French striker Olivier Giroud celebrates scoring the equalising goal to make it 1-1

The home side refused to be sucked into a tit-for-tat battle of the tippy-tappy that some might have expected. Arsenal, in any case, relied on a favourite set piece for their only chance of the first half in the 44th minute, Mesut Özil’s corner being flicked on by Mertesacker for Koscielny, who brought a good save from Artur Boruc to his left.

Unlike their hosts, Arsenal’s form line had been strong: seven straight wins in the Premier League and FA Cup since a draw against Chelsea on 23 December. But after meeting Crystal Palace next Sunday the leaders face all six of the teams immediately below them in the table during a daunting nine-week fixture list that also includes Liverpool in the FA Cup and Bayern Munich in the Champions League.

A point or three here looked imperative, given all that. And two Arsenal goals in the opening five minutes of the second half suggested Wenger had made that clear too.

Santi Cazorla of Arsenal celebrates scoring their second goal with Olivier Giroud

Giroud’s status as the prime striker has been accompanied by persistent mickey-taking of their understudy Nicklas Bendtner that even reached the BBC’s The Graham Norton Show last Friday when the comedian Lee Mack teased Thierry Henry about the Dane. The rumour mill has Arsenal targeting strikers or an attacking midfielder such as Schalke’s Julian Draxler.

It did not bother the Frenchman, though, as he plundered his 10th league goal in a season’s total of 14. A long cross was muscled on by Bacary Sagna, shrugging off Jack Cork, and the full-back’s low cross was cutely nudged in off Giroud’s heel. Soon afterwards, Özil strode down the right-hand side, stepped inside Cork and passed sideways for Cazorla – with more than a hint of a scuff – to shoot past Boruc.

Southampton’s response, mercifully for them, was immediate. With 54 minutes gone Sagna was foxed by a pass over his head that Jay Rodriguez latched on to before dinking a nice ball for his fellow England new boy Lallana to smash home with his left foot.

Adam Lallana of Southampton celebrates scoring their second goal against Arsenal

Özil, emboldened, had a shot deflected on to the top of the bar. The German was then fouled by Morgan Schneiderlin but the free-kick was lofted to nowhere in particular in an echo of Arsenal’s earlier torpor. At the other end Szczesny raced out to toe a dangerous through ball away from Rodriguez.

The temperature of the match had dropped a few degrees once the scores were level but that changed with 11 minutes remaining when Mathieu Flamini was shown a straight red card for a two-footed lunge on Schneiderlin. Shaw’s attacking quality was shown again with a shot nicked off Sagna that Szczesny turned over the bar and from the corner, the Pole palmed away Fonte’s volley.

Before that November meeting these clubs were three league points apart; now it is 20, but Arsenal’s upward momentum stalled here.